Phase locked loops are used in a wide variety of applications. For example, phase locked loops are routinely used in communication devices to provide clock signals to various components of the devices. A conventional phase locked loop includes a charge pump that controls a reference voltage used by an oscillator to produce an output signal. Conventional charge pumps typically generate “up” and “down” currents to control the reference voltage.
A problem with conventional phase locked loops is that the output signals suffer from unwanted spurious signals. These spurious signals can negatively affect the components that use the output signals. For example, communication devices often use phase locked loops to transmit and receive data. Unwanted spurious signals may disturb data being received and introduce unwanted spectral content into data being transmitted.
The charge pumps are often the dominant component that determines the level of unwanted spurious signals in the output signals generated by the phase locked loops. A common cause is a mismatch between the “up” and “down” currents generated by the charge pumps.